1. Field of the Invention
The present invention relates generally to a hybrid powertrain system for motor vehicles and, more particularly, to an electronically controlled transmission for hybrid powertrain system for a motor vehicle.
2. Description of the Related Art
Since the invention of power vehicles, many different powertrain systems have been attempted, including a steam engine with a boiler or an electric motor with a storage battery. It was, however, the discovery of petroleum in 1856 and the four-stroke internal combustion engine invented by Otto in 1876, that provided the impetus for the modern motor vehicle industry. Although fossil fuel emerged as the fuel of choice for motor vehicles, recent concerns regarding fuel availability and increasingly stringent federal and state emission regulations have renewed interest in alternative fuel powered vehicles. Alternative fuel vehicles include vehicles powered by methanol, ethanol, natural gas, electricity, or a combination of these fuels.
Of these vehicles, electrically powered alternative fuel vehicles offers several advantages: electricity is readily available, an electric power distribution system is already in place, and an electric powered vehicle produces virtually no emissions. There are, however, several technological disadvantages that must be overcome before electric powered vehicles gain acceptance in the marketplace. For instance, the range of an electric powered vehicle is limited to approximately 100 miles, compared to approximately 300 miles for a similar fossil fuel powered vehicle. Further, the acceleration is significantly less than that of a comparable fossil fuel powered vehicle.
A hybrid powered vehicle, powered by both a fuel source and an energy storage device, overcomes the technical disadvantages of a dedicated electric vehicle while still offering an environmental benefit. The performance and range characteristics of the hybrid powered vehicle is comparable to a conventional fossil fuel powered vehicle. Thus, there is a need in the art for hybrid powertrain system for a motor vehicle that is energy efficient, has low emissions, and offers the performance of a conventional fossil fuel powered vehicle. Further, there is a need for a transmission system to complement the combined electric and gas power plants.
There are presently two transmissions available for use on conventional automobiles. The first, and oldest, type of transmission is the manually operated transmission. These transmissions are characterized in that vehicles having manually operated transmissions include a clutch pedal usually positioned to the left of the brake pedal and a H configuration gear shift lever which is usually mounted in the center of the vehicle just behind the dashboard. To operate the manual transmission, the driver must coordinate depression of the clutch and accelerator pedals with the position of the shift lever in order to shift into the desired gear. Proper operation of a manual transmission is well known to those of skilled in the art, and will not be described further herein.
In a vehicle having an automatic transmission, no clutch pedal is necessary, and the standard H configuration shift lever is replaced by a shift lever which moves back and forth for gear selection. The driver need only select between park, reverse, neutral, drive, and 1 or 2 low gears then operate an accelerator and a brake pedal. As it is commonly known in the art, the shift lever is placed in one of several positions having the designation P, R, N, D, 2, and possibly 1, which corresponds to park, reverse, neutral, drive, and first or second low gears, respectively. Vehicle operation when the gear shift lever is placed in one of these positions is well know in the art. In particular, when in drive mode, the transmission automatically selects between the available forward gears. As is also well known, older transmission systems typically included first, second, and third gears, while newer transmission systems include first through third gears as well as a fourth and possibly a fifth overdrive gears. The overdrive gears provide improved fuel economy at higher speeds.
Early transmissions were almost exclusively manually operated transmissions. With a steady development of automatic transmissions, drivers increasingly gravitated toward the ease of operation offered by automatic transmissions. However, in the middle 1970's, heightened concerns about present and future fossil fuel shortages resulted in implementation of corporate average fuel economy regulations. These fuel economy requirements necessitated investigating increasing the fuel economy of motor vehicles in order to meet government regulations. These government regulations prompted further investigation of and a renewed interest in transmission efficiency.
In the ensuing years, many mechanical vehicle systems were adapted to include electronic actuator mechanisms to replace the mechanical actuators or, alternatively, were adapted to be electronically controlled. The electronic control systems greatly increased the fuel efficiency of vehicle engines and enabled a gradual reversion to the convenience of automatic transmissions. In addition, electronic controls placed on automatic transmissions greatly improved the shift schedules and shift feel of automatic transmissions and also enabled acceptable implementation of fourth and fifth overdrive gears, thereby increasing fuel economy. Thus, automatic transmissions have become increasingly popular.
Automatic and manual transmissions offer various competing advantages and disadvantages. A manual transmission enables the driver to select particular forward gears, depending upon the driving conditions. For example, the driver may shift from fifth to third when needing additional power in order to quickly accelerate the vehicle, such as in a passing situation. Manual transmissions also provide the driver with greater control of vehicle acceleration, because the driver may maintain the transmission in a lower forward gear for continued acceleration. On the other hand, an automatic transmission may upshift when the driver does not desire such an upshift, thereby limiting vehicle acceleration. Further, skilled drivers can take advantage of weight distribution between the front and rear tires by selectively upshifting and downshifting when entering and exiting curves and corners. Finally, some drivers prefer the sporty impression that manual transmissions provide. Conversely, automatic transmissions first and foremost offer ease of operation, so that the driver need not burden both hands, one for the steering wheel and one for the gear shifter, and both feet, one for the clutch and one for the gas and brake while driving. When operating an automatic transmission the driver has one hand and one foot free. In addition, an automatic transmission provides extreme convenience in stop and go situations, as the driver need not worry about continuously shifting gears to adjust the ever-changing speed of traffic.
With respect to hybrid vehicles, however, manual transmissions prove to be particularly advantageous to increasing efficiency, thereby improving fuel economy. The primary reason for the superior efficiency of the manual transmission in the hybrid vehicle lies in the basic operation of automatic transmissions. In most automatic transmissions, the output of the engine connects to the input of the transmission through a torque converter. Most torque converters have an input turbine connected to the output shaft of the engine and an input turbine connected to the input shaft of the transmission. Movement of the turbine at the input side results in a hydraulic fluid flow which causes a corresponding movement of the turbine connected to the input shaft of the transmission. While torque converters provide a smooth coupling between the engine and the transmission, hydraulic fluid inherently introduces parasitic losses, thereby decreasing efficiency of the powertrain. Further, the shift operation in an automatic transmission also requires hydraulic fluid pressure, thereby introducing additional parasitic losses and efficiency in the powertrain. Thus, there is a need in the art for a powertrain system having an efficient transmission which limits parasitic losses due to hydraulic fluid control.
Thus, it is an object of the present invention to provide a hybrid powertrain system for a motor vehicle.
It is another object of the present invention to provide a hybrid powertrain system having an improved power distribution system.
It is yet another object of the present invention to provide a transmission for a hybrid powertrain system which eliminates parasitic losses due to hydraulic fluid flow which occurs in a typical automatic transmission.
It is yet another object of the present invention to provide an automatic transmission for a hybrid powertrain system which configured substantially as a manually operated transmission.
It is yet another object of the present invention to provide a transmission for a hybrid powertrain system which is configured as a manual-style transmission and is electronically controlled to substantially operate as an automatic transmission, thereby eliminating parasitic loses due to hydraulic fluid flow.
It is yet another object of the present invention to provide a hybrid powertrain transmission system that utilizes an electric machine to synchronize the speed of the driving or input shaft of the transmission with the speed of the driven or output shaft of the transmission.
It is yet another object of the present invention to provide a hybrid powertrain transmission system that utilizes an electric machine to reduce the speed of the driving or input shaft of the transmission in order to synchronize the input shaft speed with the driving or output shaft speed and which operates in a regenerative mode to output electricity when reducing the speed of the input shaft.
It is yet a further object of the present invention to provide a hybrid powertrain transmission system that utilizes an electric machine to synchronize the speed of the driving or input shaft with the speed of the driven or output shaft of the transmission by increasing the speed of the input shaft in order to synchronize the speeds of the input and output shafts.
It is yet a further object of the present invention to provide a hybrid powertrain transmission system having a set of electric motors to effect depressing a clutch of a manual-style transmission and to effect shifting gears of a manual-style transmission.
It is yet another object of the present invention to provide a hybrid powertrain transmission system having electric motors to effect operation of the clutch and shifting a of the gears of a manual-style transmission in accordance with electronic control signals generated by a transmission controller.